The invention refers to an apparatus for testing gears by rolling without backlash with a mating gear according to the preamble of claim 1. An apparatus of this kind is known from DE 34 15 631 C2.
Such apparatus are frequently used in automated gear production lines, for instance to test previously hobbed gear teeth before the next working step is performed on the same workpiece. This can prevent that a severely malformed gear is unnecessarily further processed or impedes the next working step, causes increased tool wear or even destroys the tool. Such a gear is discovered on time and removed from production as a result of the test.
For this purpose, each gear is automatically fed to a tester and is clamped on a motor-driven spindle having a stationary axis of rotation. A mating gear, or master gear, which loosely rotates on an oscillating slide, is advanced towards the test gear from a secure parking position and is automatically brought into mesh with the test gear. After the teeth of both gears got double flank contact, the oscillating slide is displaced somewhat against a spring force, so that an adequate test force exists at the so-called test center distance xe2x80x9caxe2x80x9d. Then the spindle makes at least one full revolution with the test gear wherein the mating gear follows in tight mesh. Gearing deviations cause the oscillating slide to reciprocate in the direction of the center distance. These center distance variations are measured and, if a given upper or lower tolerance limit is passed, the tested gear is sorted out.
Obviously, such automatic testing apparatus are continuously further developed. The major selective criteria for this are high operational reliability, adaptability to different tooth systems, and test results containing as much information as possible. For example, numerous testers are already known that can be used for the described double flank rolling test. Here are only a few:
The double flank rolling tester according to DE 34 15 631 C2 has automatically operated engaging means characterized in that the loosely following mating gear is held in a specific rotary position by a magnet which is oriented toward a tooth of the mating gear, and that the work gear is assigned to a positioning device likewise working with a magnet or a sensor. This is to guarantee that for engaging, a tooth of the mating gear precisely matches with a tooth gap of the test gear. Aside from this, the tester as shown in FIG. 6 of this published patent has the classic design, namely the movable first slide 14 is biased by a mechanical spring F and located on a second slide 16 which in turn is slidably mounted on a flat guide 18 of the base 2 in order to set the test center distance. The publication does not reveal whether a pneumatic cylinder or a stepping motor with threaded spindle is provided for this setting. The center distance deviations xc2x1xcex94a are measured according to FIG. 6 with a conventional electric probe.
The more recent utility model DE 200 05 299 U1 refers to an apparatus for quality testing of gears. In addition to a measuring unit that operates according to the single flank or double flank rolling principle and that has a master gear and a clamping device, this apparatus also has conveyor means for feeding the test pieces to the clamping device and for removing them after the rolling test. Its primary features are that the master gear and the test gears mounted on the clamping device rotate about vertical axes, and that the conveyor means has a gripper for grasping the test gears. Thus, the measuring unit hardly differs from the tester of DE 34 15 631 C2 described above, with two exceptions: According to FIG. 6 of this publication, the oscillating slide 34 is not disposed on the slide 30, but rather both slides are arranged one after the other on the base plate 28; they are guided so as to be moved longitudinally in the same direction; and they are interconnected solely through spring means. This is intended to allow greater precision of the discoupled oscillating slide. Also, in this way the accelerations of the oscillating slide 34 during rolling of the gears are said to be more exactly measured by the sensor 38 than is generally the case if the center distance variations are measured with a linear encoder.
A further, known xe2x80x9ctesting machine, especially for gearsxe2x80x9d (DE 29 33 891 C2) deals with the accuracy and evaluation of measured signals from the center distance variations recorded by a sensor. This involves circuits for a now obsolete carrier frequency measuring amplifier. This publication is only significant for the prior art insofar as FIG. 4 contains the schematic representation of a cardan-suspended probe to be used for measuring helix deviations and taper of the gear teeth. However, this probe is very complex in design and is not suitable for use in automated production lines.
The invention xe2x80x9cAutomatic Gear Checking Structure and Methodxe2x80x9d according to U.S. Pat. No. 4,488,359 is an improvement over the foregoing patent specification, since variations in the angle of rotation of the master gear relative to the test gear are to be measured in addition to the center distance variations, to enhance the validity of the measurement. To be sure, the circuits described here are somewhat more modern, but the mechanical design of the apparatus, which again is only schematically shown, has hardly been developed further. According to its FIG. 3, the master gear 40 is held in a fork 66 so as to rotate about its horizontal axis 98. The fork 66 merges into a cylindrical shaft 68 which in turn is easily pivotable about the axis 96 and adapted to be easily displaceable in the same bearing in the longitudinal direction 90. Inductive positional transducers 20 and 22 are to record the movements that may occur in the testing process. In this invention, however, no second slide or corresponding means is provided by which another test center distance could be set, for instance to test gears with larger diameters. Instead, there is a slide 44 which supports a rotatable spindle 51 and which can be reciprocated coaxially to the second spindle 58 by a working cylinder 48. The test gears 38, which have a center bore, are automatically centered and clamped by this means. For this purpose an inclined ramp 36 is provided, on which the test gears are fed by gravity to the testing apparatus. After testing the slide 44 moves back, the test gears are released and fall for further transport onto a second inclined ramp 42.
A double flank rolling tester is known from DE 42 31 275 A1, in which a mounting device supporting a master gear or a test gear can be driven linearly relative to a device base by a motor and an acme threaded spindle.
Double flank rolling testers differ significantly from single flank rolling testers in which gears are tested at a fixed center distance. In the latter case only one flank of any tooth comes into contact when the two gears are rotated, and the instantaneous angle deviation of the driven gear is measured relative to the theoretically correct angular position resulting from the transmission ratio. For example, a device of this type is described in the U.S. Pat. No. 3,358,374.
In other types of measuring devices that are neither double flank nor single flank rolling testers there are developments utilizing linear motors, for instance to position a probe in X, Y, and Z directions. They replace the conventional combination of electric motor and ball screw, such as those frequently used in 3D measuring devices. A particularly precise, but very complex solution is described in DE 38 23 978 A1. In this linear guide means for precision machines the movable part is supported relative to the stationary part by magnetic or air bearings and the electrically driven linear motor is engineered to be superconducting, so that the heat losses in the magnet coils do not affect the accuracy of the measuring device. This can be necessary for absolute longitudinal measurements in coordinate measuring devices, but it is not worthwhile for relative measurements like center distance variations in the double flank rolling test.
Scanning heads for coordinate measuring devices (such as in EP 0 693 669 A2) include power generators mounted on the leaf spring guides of the scanning element for the three displacement directions X, Y, Z. These power generators each generate a measuring force together with the leaf springs. They are also used for damping or even clamping in one of the displacement directions. These power generators comprise a coil and a magnet as the core, and they thus use the same physical effect as a linear motor; however, the maximum traveling distances are less than 1 mm.
The scanner head with an electronic guide according to DE 196 41 720 A1 is very similarly designed. It is characterized in that its driving device binds the probe by means of the power generators to an area with a curved contour, preferably on a spherical surface. This should enable the scanner head to determine not only the space coordinates but also the normal of an unknown workpiece surface at the measured point in question. In this invention, the magnet cores likewise move only over very short distances in their coils, which are also referred to in the publication as electromagnetic direct drives. For this reason, this type of drive can not be used in double flank rolling testers.
In the light of this state of the art, the object of the invention is to further simplify the design of a double flank rolling tester, especially for the automatic test run in production lines, without restricting proven functions of the known testing devices.
This object is achieved in accordance with the invention by an apparatus for testing gears by rolling without backlash with a mating gear, generally a master gear, comprising a base, having
a stationary spindle on which a test gear can be mounted and which can be driven numerically controlled by a motor with a coaxial rotary encoder
an oscillating slide on which a rotary mounting device is located with either a fixed or a self-aligning axis of rotation for loosely rotating the mating gear, said slide being guided for easy movement in the direction of the center distance of the two gears,
characterized in that the stationary part of a linear motor is disposed on the base and the movable part thereof is disposed to the oscillating slide, and that an associated computer numerically controlled (CNC) is provided to allow the linear motor to be used for said three means.
The base of the novel testing apparatus preferably supports the longish stationary part of a linear motor and the shorter movable part is disposed to the oscillating slide. The control of the linear motor is designed not only to permit a specified test center distance to be set, but also so that a specifiable test force is generated by the linear motor and center distance variations are recorded.
The simplification and cost reduction that are thereby achieved in the design and assembly of the double flank rolling tester are obvious. The conventional second slide that adjusts the oscillating slide to the test center distance is omitted altogether. The linear motor is not only used to position the oscillating slide, but it also replaces the conventional, usually mechanical springs. With the aid of the CNC control it is possible to set the amount of test force that is optimal for the test gears and to keep it constant even over the whole range of the center distance variations. Furthermore, the linear measuring system provided at each linear motor is additionally used to measure the center distance variation which occurs when rolling without backlash, and to have the measured values stored and evaluated by the CNC control. Finally, manual settings in conventional automatic double flank rolling testers, such as limit switches, stops or the like, are eliminated in that they are programmed once in the CNC control of the linear motor for a specific test gear/master gear combination, then they are stored and made available on call with the same accuracy.
In a preferred embodiment of the invention, the longish stator comprising a series of coils is provided as the stationary part of the linear motor and the short runner of the linear motor, made up of only a few permanent magnets, is provided as the movable part. The advantage in a double flank rolling tester lies in the space-saving arrangement of this linear motor type. A further advantage is that the easily movable oscillating slide requires no energy supply through a cable and that the heat occurring in the coils can be more easily removed through the base than from the slide.
In a further embodiment of the invention the mating gear is mounted in pendulum fashion on the oscillating slide by means of a central ball and a corresponding calotte, and the angular displacements of its axis of rotation during backlash-free rolling with the test gear can be measured with two displacement sensors arranged perpendicularly to one another and to the nominal position of the axis of rotation. In this simple manner helix deviations and taper on the test gear can also be determined with the testing apparatus according to the invention. To simultaneously measure these deviations together with the double flank rolling deviations Fixe2x80x3, and fixe2x80x3, two oscillating slides opposite to one another are preferably provided at the stationary spindle of the testing apparatus. One of the oscillating slides carries the mating gear with the fixed axis of rotation, and the other carries a second mating gear with the self-aligning axis of rotation. This combination can be implemented in advantageous manner especially with oscillating slides equipped with linear motors according to the invention.